JP3681953B2 - Film thickness measuring method and film thickness measuring apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention covers a first thin film such as an oxide film formed on a substrate such as a semiconductor wafer and polishes a metal film such as a copper film different from the first thin film by a CMP (chemical mechanical polishing) process. The present invention relates to a film thickness measuring method and a film thickness measuring apparatus for measuring a film thickness of a metal film in a process of removing a predetermined amount by the method and exposing a layer including a first thin film.
[0002]
[Prior art]
In recent years, as a method of forming a predetermined circuit pattern on a semiconductor wafer (hereinafter referred to as a substrate), an oxide film formed in a predetermined pattern on a substrate is covered and a copper film is embedded in a recess between the oxide films. After the copper film is formed, a damascene process is used in which the copper film is polished and removed from the surface by a predetermined amount by CMP to expose the layer including the oxide film and the copper film embedded in the recess between the oxide films. Has been.
[0003]
The CMP process is performed in a state where the substrate surface is pressed against the polishing cloth stretched on the turntable while the substrate is held by the top ring so that the surface of the substrate on which the copper film is formed is directed downward. . In this state, slurry (polishing abrasive liquid) is supplied onto the polishing cloth, and the turntable and the top ring are independently rotated by a motor.
[0004]
The polishing process (removal process) is terminated when the copper film is removed by the CMP process and a layer including an oxide film is exposed. The end point of the polishing process is obtained, for example, as follows. The frictional force between the surface of the substrate held by the rotationally driven top ring and the polishing cloth on the rotationally driven turntable is oxidized when the surface of the substrate is a copper film and when the copper film is removed. It varies depending on when a layer including a film or the like is exposed. The load (torque) applied to the motor that rotationally drives the top ring and the turntable independently varies according to the change in the frictional force. The point at which the load on the motor changes in this way is defined as the end point of the polishing process.
[0005]
[Problems to be solved by the invention]
However, as described above, when the end point of the polishing process is determined by the change in the load on the motor, the layer including the oxide film or the like is polished more than necessary between the time when the end point is calculated and the polishing process is stopped. The problem of being removed.
An object of the present invention is to measure the film thickness of a metal film in the course of a removal process such as a polishing process in order to prevent the layer including the first thin film from being removed more than necessary in view of the above points. It is in providing the film thickness measuring method and film thickness measuring apparatus which can do.
[0006]
[Means for Solving the Problems]
Process invention to the second thin film covering the first thin film formed on the substrate is removed by a predetermined amount to expose the layer containing the first thin film according to claim 1 to solve the above-described problems In the film thickness measuring method for measuring the film thickness of the second thin film, the first thin film is a transparent film with respect to the measurement light, and the second thin film has a thickness greater than a predetermined value. The substrate is a substrate in which the first thin film is formed in a predetermined pattern and then the predetermined metal is embedded between the patterns to form the second thin film. A storage step of storing a spectral reflection spectrum of the predetermined metal film with respect to the measurement light having a film thickness thicker than the predetermined value; and the substrate from which the second thin film is removed by less than the predetermined amount. the irradiated with measurement light Te, the measuring light irradiation A metering step of determining the spectral reflection spectrum of the substrate based on the light reflected from the substrate that is, the predetermined metal film stored in the photometry process at the storage step and the spectral reflectance of the substrate obtained In the comparison step for comparing the spectral reflection spectra of the second thin film and the spectral reflection spectrum of the predetermined metal film in the comparison step, the film thickness of the second thin film is not matched. And a film thickness calculating step of calculating a film thickness of the second thin film based on a spectral reflection spectrum of the substrate.
[0008]
Invention, the first second covering the thin film of the second thin film in the process of exposing a layer containing a predetermined amount of the first thin film is removed which is formed on a substrate according to claim 2 In the film thickness measuring apparatus for measuring a film thickness, the first thin film is a transparent film with respect to measurement light, and the second thin film is made of a predetermined metal that does not transmit the measurement light at a film thickness larger than a predetermined value. The substrate is a substrate in which the first thin film is formed in a predetermined pattern and the second thin film is formed by embedding the predetermined metal film between the patterns. Storage means for storing a spectral reflection spectrum of the predetermined metal film with respect to the measurement light having a film thickness thicker than a value; and the measurement light for the substrate from which the second thin film is removed by less than the predetermined amount. irradiated, anti from the substrate on which the measuring light is irradiated Was a photometric means for determining the spectral reflection spectrum of the substrate based on the reflected light, and a spectral reflection spectrum of the predetermined metal film stored in the spectral reflection spectrum of the substrate and the storage step was determined by the photometric means The film thickness of the second thin film is less than or equal to the predetermined value when the spectral reflection spectrum of the substrate and the spectral reflection spectrum of the predetermined metal film are inconsistent by the comparing means for comparing and the comparing step . And a film thickness calculating means for calculating the film thickness of the second thin film based on the spectral reflection spectrum of the substrate.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0011]
<Configuration of film thickness measuring device>
FIG. 1 is a schematic view showing a film thickness measuring apparatus which is one embodiment of the present invention. The stage 1 holds a substrate carried in from a CMP processing apparatus (not shown) horizontally and is configured to be movable in a horizontal plane. The light source unit 3 includes a lamp 3a including a halogen lamp or a deuterium lamp, and a plurality of lenses 3b, and emits visible light or ultraviolet measurement light.
[0012]
The beam splitter 5 reflects the measurement light emitted in the lateral direction from the light source unit 3 in the downward direction and transmits the reflected light reflected from the substrate W and transmitted through the objective lens 7. The objective lens 7 irradiates the measurement light reflected by the beam splitter 5 to a predetermined region including the measurement region R on the substrate W. The size of the measurement region R is set by the magnification of the objective lens 7 and the size of a pinhole formed in the plate 11a described later, and is approximately several μm to several tens of μm in diameter.
[0013]
The tube lens 9 condenses the reflected light reflected from the measurement region R of the substrate W and transmitted through the objective lens 7 and the beam splitter 5 toward the spectroscopic unit 11. The spectroscopic unit 11 is disposed above the plate 11a having a pinhole formed at the incident position of the reflected light collected by the tube lens 9, and passes through the pinhole and enters the spectroscopic unit 11. A concave diffraction grating 11b that splits the reflected light and a photodetector 11c that detects the spectral light intensity of the diffracted light split by the concave diffraction grating 11b. The photodetector 11c is configured by, for example, a photodiode array or a CCD, and is arranged in a conjugate relationship with the pinhole of the plate 11a. Further, the spectral light intensity detected by the light detector 11 c is output to the data processing unit 19.
[0014]
The data processing unit 19 performs processing according to a control signal output from the control unit 23 having a built-in CPU and memory based on an instruction from the operator via the operation unit 27. Specifically, the spectral reflection spectrum N (λ) based on the spectral light intensity of a metal film such as a copper film detected by the photodetector 11c and the reflection from the measurement region R of the substrate W detected by the photodetector 11c. A spectral reflection spectrum M (λ) based on the spectral light intensity of light is obtained, and these spectral reflection spectra N (λ) and M (λ) are stored. Further, the stored spectral reflection spectrum N (λ) of the metal film is compared with the spectral reflection spectrum M (λ) of the substrate W, and a predetermined process described later is executed according to the comparison result.
[0015]
The prism 13 disposed between the tube lens 9 and the spectroscopic unit 11 extracts part of the reflected light from the substrate W. A part of the extracted reflected light is guided to the imaging unit 15. The imaging unit 15 captures a lens 15a that condenses a part of the reflected light toward the image sensor 15b, images the light collected by the lens 15a, and outputs an image signal corresponding to the measurement region to the image processing unit 17. And an image sensor 15b that outputs to the image sensor.
[0016]
The image processing unit 17 performs predetermined processing on the image signal input from the image sensor 15 b and outputs the processed image signal to the I / O 21. The output image signal is output to the display device 25 under the control of the control unit 23 to display an image. While viewing the image, the operator operates the operation unit 27 to move the stage 1 to set a measurement region at a desired position on the surface of the substrate W.
[0017]
The data processing unit 19 and the like described above correspond to the storage unit, the comparison unit, and the film thickness calculation unit of the present invention, and the spectroscopic unit 11 and the like correspond to the photometry unit of the present invention.
[0018]
<Thin film state on substrate W>
Here, an example of a thin film state formed on the substrate W in the CMP process will be described. FIG. 2 is a plan view showing a thin film state in the vicinity of the measurement region R on the substrate W. FIG. FIG. 3 is a longitudinal sectional view showing a thin film state in the vicinity of the measurement region R of the substrate W before the CMP process.
[0019]
As shown in FIGS. 2 and 3, an oxide film F1 having a predetermined pattern is formed on a silicon substrate Wa which is a base of the substrate W, and a barrier metal film F2 such as tantalum nitride (TaN) is deposited thereon. Further, a copper film F3 for copper wiring is deposited so as to cover the upper portion and fill the concave portion of the oxide film F1. The oxide film F1 described above is a transparent film for the measurement light and corresponds to the first thin film of the present invention.
[0020]
The spectral reflection spectrum for the measurement light of the substrate W shown in FIG. 3 is, for example, a spectral reflection spectrum N (λ) that rises to the right as shown in FIG. The spectral reflection spectrum N (λ) is composed of only the component due to the reflected light from the surface of the copper film F3 because the measurement light does not pass through the copper film F3 in the measurement region R because the copper film F3 is thick. Has been. The spectral reflection spectrum N (λ) is composed of a relative reflection ratio with respect to the silicon substrate Wa at each wavelength of the measurement light.
[0021]
FIG. 4 shows a state in which the copper film F3 on the substrate W shown in FIG. 3 is polished and removed from the surface by a predetermined amount by a CMP processing apparatus (not shown). In FIG. 4, a thickness dimension d4 from the surface of the copper film F3 to the upper surface of the barrier metal film F2 formed on the oxide film F1 is, for example, 50 nm.
[0022]
FIG. 5 shows a state where the substrate W shown in FIG. 4 is further polished and the polishing process is completed. At the end of this polishing process, the upper surface of the oxide film F1 on the substrate W is exposed.
[0023]
The spectral reflection spectrum with respect to the measurement light of the substrate W (FIG. 5) after the polishing process is, for example, a spectral reflection spectrum M (λ) as shown in FIG. This spectral reflection spectrum M (λ) is a component of the spectral reflection spectrum from the exposed portions of the oxide film F1 and the barrier metal film F2, and the spectral reflection spectrum from the copper film F3 embedded in the recess of the oxide film F1. There are multiple valleys that combine ingredients. That is, since the measurement light is transmitted through the oxide film F1 and the barrier metal film F2 in the portion where the oxide film F1 and the barrier metal film F2 are exposed, the spectral reflection spectrum of this portion is from the surface of the oxide film F1 or the barrier metal film F2. The reflected reflected light and the reflected light reflected from the silicon substrate Wa are composed of components that interfere with each other, and there are a plurality of peaks and valleys in the spectral reflection spectrum. Since the copper film F3 embedded in the recess of the oxide film F1 has a large thickness dimension and does not transmit the measurement light, the spectral reflection spectrum from this part is composed only of the reflected light from the copper film F3. The spectral reflection spectrum N (λ) as shown in FIG. Therefore, the spectral reflection spectrum M (λ) for the measurement light of the substrate W in the measurement region R shown in FIG. 5 is the spectral reflection spectroscopic component due to the exposed portions of the oxide film F1 and the barrier metal film F2, and the surface of the copper film F3. The spectral reflection spectrum M (λ) is combined with the spectral reflection spectrum component from the above, and has a plurality of peaks and valleys.
[0024]
<Operation of film thickness measuring device>
The operation of the film thickness measuring apparatus will be described with reference to the flowchart of FIG.
[0025]
Step S1 (preparation process)
First, the operator places the substrate W before the polishing process shown in FIG. 3 on the stage 1 and confirms an image displayed on the display device 25 while operating the operation unit 27, so that a desired one on the substrate W is obtained. The measurement area R is set at the position. Next, the measurement light from the light source unit 3 is irradiated onto the measurement region R of the substrate W through the beam splitter 5 and the objective lens 7. The measurement light irradiated to the measurement region R is reflected on the surface of the copper film F3 without passing through the copper film F3 because the thickness dimension of the copper film F3 is large. The reflected light reflected from the measurement region R enters the spectroscopic unit 11 through the objective lens 7, the beam splitter 5, the tube lens 9, and the like. The reflected light incident on the spectroscopic unit 11 is split and the light intensity is output to the data processing unit 19. The data processing unit 19 creates and stores a spectral reflection spectrum N (λ) of the copper film F3 shown in FIG. 6, for example, based on the input spectral light intensity.
[0026]
Step S2 (polishing process)
The substrate W (FIG. 3) that has completed the preparation process (step 1) is set in a CMP processing apparatus (not shown). Then, the surface of the copper film F3 of the substrate W is polished and removed to a middle point just before the end point of the polishing process by the CMP processing apparatus, and the polishing process is temporarily interrupted.
[0027]
Step S3 (photometric process)
The operator places the substrate W at the intermediate point on the stage 1 and confirms the image displayed on the display device 25 while operating the operation unit 27 to set the measurement region R at a desired position on the substrate W. Set. Next, the measurement light from the light source unit 3 is irradiated onto the measurement region R of the substrate W through the beam splitter 5 and the objective lens 7. The reflected light reflected from the measurement region R enters the spectroscopic unit 11 through the objective lens 7, the beam splitter 5, the tube lens 9, and the like. The reflected light incident on the spectroscopic unit 11 is split and the spectral light intensity is output to the data processing unit 19. The data processing unit 19 creates and stores a spectral reflection spectrum M (λ) of the substrate W based on the input spectral light intensity.
[0028]
Steps S4 and S5 (comparison process)
Next, in step S4, the spectral reflection spectrum N (λ) of the copper film F3 created in the preparation process of step S1 in the data processing unit 19 and the spectral reflection spectrum M (λ) of the substrate W created in the photometry process of step S3. Compare Based on the comparison result, the process branches from step S5. That is, when it is determined in step S5 that the spectral reflection spectrum N (λ) of the copper film F3 and the spectral reflection spectrum M (λ) of the substrate W are inconsistent with each other, the process proceeds to the next step S6.
[0029]
The spectral reflection spectrum N (λ) of the copper film F3 and the spectral reflection spectrum M (λ) of the substrate W do not coincide with each other because the thickness dimension of the copper film F3 is a predetermined value or less and a part of the measurement light. Is transmitted through the copper film F3, the spectral reflection spectrum N (λ) of the substrate W before the polishing process shown in FIG. 6 is added to the spectral reflection spectrum M (λ) of the substrate W after the polishing process shown in FIG. Is added. Specifically, as shown in FIG. 4, when the thickness dimension d4 from the surface of the copper film F3 to the upper surface of the barrier metal film F2 formed on the oxide film F1 is, for example, 50 nm or less, the measurement light is copper in this portion. The light passes through the film F3 and reaches the barrier metal F2, the oxide film F2, and the silicon substrate Wa. As a result, the spectral reflection spectrum M (λ) of the substrate W at the intermediate point shown in FIG. 4 is changed from the spectral reflection spectrum N (λ) of the copper film F3 shown in FIG. 6 to the spectral reflection spectrum M (λ) shown in FIG. It becomes a spectral reflection spectrum during the transition to, and has a plurality of peaks and valleys.
[0030]
In step S5, the spectral reflection spectrum N (λ) of the copper film F3 and the spectral reflection spectrum M (λ) of the substrate W are not inconsistent with each other, that is, the spectral reflection spectrum N (λ) of the copper film F3 and the substrate W. When it is determined that the spectral reflection spectra M (λ) of the two coincide with each other, the process returns to step S2. In this case, the thickness dimension d4 shown in FIG. 4 exceeds 50 nm, for example, and there is no portion where the measurement light passes through the copper film F3 over the entire measurement region R. Therefore, the spectral reflection spectrum M (λ) from the substrate W in this case is equal to the spectral reflection spectrum N (λ) of the copper film F3 shown in FIG. In this case, it is determined that the polishing process is insufficient under the initially set polishing process condition, and the process returns to the polishing process in step S2, and the thickness dimension d4 is, for example, 50 nm or less and immediately before the oxide film F1 is exposed. Then, the polishing process conditions are reset so that the polishing process is performed again.
[0031]
Step S6 (film thickness calculation step)
In step S6, the thickness dimension d4 shown in FIG. 4 is calculated. In the portion where the oxide film F1 shown in FIG. 4 is formed, a copper film F3, a barrier metal film F2, and an oxide film F1, which are transparent films for the measurement light, are formed on the silicon substrate Wa. In other words, three multilayer films of the oxide film F1, the barrier metal film F2, and the copper film F3 are formed on the silicon substrate Wa. As a method for calculating the film thickness of each thin film in such a multilayer film, for example, a method described in Japanese Patent No. 2866559 is known.
[0032]
When this method is executed by the above-described film thickness measuring apparatus, first, the operator first counts the number of thin films in the multilayer film (in this embodiment, “3” of the oxide film F1, the barrier metal film F2, and the copper film F3) and each thin film. The optical constant is input via the operation unit 27 and stored in the data processing unit 19. Next, the total number of peaks and valleys (peak / valley) of the spectral reflection spectrum M (λ) of the substrate W at the intermediate point shown in FIG. 4, the first wavelength corresponding to the peak and valley appearing on the shortest wavelength side in the wavelength range of the measurement light, and The film thickness range of each thin film is specified based on the second wavelength corresponding to the valley that appears on the longest wavelength side. Within this film thickness range, while changing the film thickness setting value of each thin film at a constant film thickness pitch, the spectral reflection spectrum when assuming that the film thickness of each thin film is the film thickness setting value and step S3 A deviation amount from the measured spectral reflection spectrum M (λ) is calculated, a combination of film thicknesses that minimizes the deviation amount is obtained, and a film thickness d4 of the copper film F3 is obtained.
[0033]
As described above, if the thickness of the copper film d4 is calculated to be, for example, 50 nm, it is possible to set the processing condition of the polishing process for exposing the oxide film F1 to be subsequently performed based on this film thickness. Therefore, it is possible to prevent the layer including the oxide film F1 on the silicon substrate Wa from being polished and removed more than necessary.
[0034]
<Other embodiments>
(1) In the above-described embodiment, the spectral reflection spectrum N (λ) of the copper film is created using the substrate W before the polishing process shown in FIG. 3 in the preparation step (step S1). The spectral reflection spectrum N (λ) of the copper film may be created using a copper film sample having a thickness. Further, the theoretical spectral reflection spectrum N (λ) of the copper film with respect to the measurement light may be stored in the data processing unit 19 via the operation unit 27 in advance. In the case of these modified examples, if the preparation process is executed in advance, it is not necessary to execute the preparation process for each substrate to be measured.
[0035]
(2) Although the above-described embodiment is applied in the polishing removal process of the copper film F3 by the CMP processing apparatus, the removal process of the copper film F3 is not limited to the polishing process. May be applied.
[0036]
(3) The film thickness measuring device described above may be incorporated in a removing device such as a polishing processing apparatus so that the film thickness can be measured in-line while performing a removing process such as a polishing process.
[0037]
(4) The stage 1 may be moved horizontally to set a plurality of measurement regions R, and the thickness of the copper film may be obtained in each measurement region R. Thus, by obtaining the film thickness of the copper film in the plurality of measurement regions R, the in-plane distribution of the film thickness of the copper film on the surface of the substrate W can be obtained. By adjusting a removing device such as a CMP processing device based on this in-plane distribution, the copper film can be removed uniformly.
[0038]
【The invention's effect】
As described above in detail, according to the first or second aspect of the invention, in the process of removing the second thin film , the spectral reflection spectrum of the predetermined metal film and the spectral reflection spectrum of the substrate do not match. Since the film thickness of the second thin film can be obtained from the spectral reflection spectrum of the substrate at that time, it is possible to prevent the layer including the first thin film formed on the substrate from being removed more than necessary.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a film thickness measuring apparatus according to an embodiment of the present invention.
FIG. 2 is a plan view of the vicinity of a measurement region R of a substrate W. FIG.
FIG. 3 is a longitudinal sectional view showing a thin film state of a substrate W before a polishing process.
FIG. 4 is a longitudinal sectional view showing a thin film state of a substrate W during a polishing process.
FIG. 5 is a longitudinal sectional view showing a thin film state of the substrate W after the polishing process is completed.
FIG. 6 is a diagram showing a spectral reflection spectrum of a copper film.
FIG. 7 is a diagram showing a spectral reflection spectrum of a substrate W after the end of a polishing process.
FIG. 8 is a flowchart showing the operation of the film thickness measuring apparatus according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Stage 3 Light source part 5 Beam splitter 7 Objective lens 11 Spectroscopic unit 19 Data processing part W Substrate Wa Silicon substrate F1 Oxide film (first thin film)
F2 Barrier metal film F3 Copper film (metal film)

Claims (2)

Film thickness measurement for measuring the second thickness of the thin film and the second film covering the first thin film formed on a substrate in the process of exposing a layer containing a predetermined amount of the first thin film is removed In the method
The first thin film is a transparent film with respect to measurement light;
The second thin film is a film of a predetermined metal that does not transmit the measurement light at a film thickness thicker than a predetermined value,
The substrate is a substrate in which the first thin film is formed in a predetermined pattern and the second thin film is formed by embedding the predetermined metal between the patterns,
A storage step of storing a spectral reflection spectrum of the predetermined metal film with respect to the measurement light having a film thickness thicker than the predetermined value;
The measuring light is irradiated to the substrate obtained by removing the second thin film by less than the predetermined amount, the measurement light is determined spectral reflection spectrum of the substrate based on the light reflected from the substrate that has been irradiated Photometric process,
A comparison step for comparing the spectral reflection spectrum of the predetermined metal film stored in the storing step and the spectral reflectance of the substrate which has been determined by the photometric process,
In the comparison step, when the spectral reflectance spectrum of the substrate and the spectral reflectance spectrum of the predetermined metal film are inconsistent, it is determined that the thickness of the second thin film is equal to or less than the predetermined value, A film thickness calculating step of calculating a film thickness of the second thin film based on a spectral reflection spectrum of the substrate;
The film thickness measuring method characterized by including. A film thickness measurement for measuring the film thickness of the second thin film in the process of removing a predetermined amount of the second thin film covering the first thin film formed on the substrate and exposing the layer containing the first thin film. In the device
The first thin film is a transparent film with respect to measurement light;
The second thin film is a film of a predetermined metal that does not transmit the measurement light at a film thickness thicker than a predetermined value,
The substrate is a substrate in which the first thin film is formed in a predetermined pattern and the second thin film is formed by embedding the predetermined metal between the patterns,
Storage means for storing a spectral reflection spectrum of the predetermined metal film with respect to the measurement light having a thickness greater than the predetermined value;
The measurement light is applied to the substrate from which the second thin film has been removed by less than the predetermined amount, and the spectral reflection spectrum of the substrate is obtained based on the reflected light reflected from the substrate irradiated with the measurement light. Photometric means;
Comparing means for comparing the spectral reflectance spectrum of the substrate obtained by the photometric means with the spectral reflectance spectrum of the predetermined metal film stored in the storing step;
According to the comparison step, when the spectral reflection spectrum of the substrate and the spectral reflection spectrum of the predetermined metal film are inconsistent, it is determined that the film thickness of the second thin film is equal to or less than the predetermined value, A film thickness calculating means for calculating a film thickness of the second thin film based on a spectral reflection spectrum of the substrate;
A film thickness measuring apparatus comprising:

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